Millions of platelet transfusions are conducted each year, yet the supply of this blood component is limited, thus patient access to treat disorders is problematic. There are also many diseases where platelet production or function are impaired, resulting in severe consequences and where there are limited clinical options available. To address these current limitations, new modes to generate functional platelets in vitro would provide a major benefit to many patients, as well as provide an approach to permit the systematic investigation of mechanisms involved in functional platelet formation. Our goal in this Project is to build upon our recent successful studies where a novel bioreactor system was engineered to house megakaryocytes (Mks) and to generate functional platelets in vitro. We will exploit this system to address our hypothesis; engineered microenvironments in vitro can be tailored to optimize the formation of functional platelets. To address the needs in the program we will: (Aim 1) establish a bioreactor-based 3D tissue system to study the mechanisms of Mk development and platelet release, with functional outcomes in terms of functional platelets generated and recovered from the system, and (Aim 2) to use this 3D tissue system to investigate mechanisms of platelet production related to biochemical signalling and environmental components (i.e. matrices, oxygen tension) as well as pathological megakaryopoiesis by including Mks from patients with platelet related diseases. With insight from this system we will be positioned to interrogate the maturation of Mks from both normal vs. diseased sources in order to begin to establish differences in Mk outcomes (adhesion, migration, proplatelet formation, platelet production and function). The outcome for the proposed study would be twofold: (1) a new laboratory model for Mk development, proplatelet formation and platelet release in normal and abnormal (disease) states, and (2) mechanistic insight into these processes. In the long run, building upon this new in vitro tissue system would allow for the more systematic understanding of the processes involved in Mk development, as well as insight into modes to intervene in disease states associated with these cells.